In order to secure a safety of the occupant, a seat belt and an air bag are provided in a motor vehicle. In recent years, in order to further improve a safety, an operation of the seat belt and the air bag is controlled by identifying an adult or a child, and further in conformity to the weight of the occupant. In particular, in the case that the occupant is an adult, a pretension of the air bag and the seat belt is actuated, and in the case that the occupant is a child, the pretension is not actuated. Alternatively, a developing gas amount and a developing speed of the air bag are adjusted and the pretension of the seat belt is adjusted in conformity to the weight of the occupant.
The identification whether the occupant is an adult or a child mentioned above is generally executed by detecting the weight by an occupant load sensor attached to a seat. As the occupant load sensor mentioned above, there are, for example, JP 11-351952 A (publication 1), JP 11-1153 A (publication 2) and JP 9-207638 A (publication 3). In each of the publications, four occupant load sensors are arranged in four corners between a floor side seat fixing member (for example, a rail mount) and a seat side fixing member (for example, a seat rail), whereby the weight of the occupant (load) is measured.
In this case, it is necessary to firmly fix the seat for the vehicle to a floor in such a manner as to be prevented from coming off at a time of an accident. In the publications 2 and 3, there is provided a structure in which the occupant load sensor is arranged between the floor side seat fixing member (for example, the rail mount) and the seat side fixing member (for example, the seat rail), and there is a risk that the occupant load sensor is broken at a time of the accident and the seat falls away. On the other hand, in the publication 1, it is intended to prevent the seat from falling away at a time of the accident by arranging a displacement regulating mechanism in addition to the occupant load sensor, however, there is a problem that the structure becomes complicated and a manufacturing cost is increased due to the independently provided displacement regulating mechanism.
In order to do away with the displacement regulating mechanism so as to restrict the manufacturing cost, the occupant load sensor can be structured, for example, as shown in FIG. 15 in place of the structure in which the seat is reciprocated vertically and the load is applied to a sensor plate as in the publication 1. FIG. 15A shows a front view of the occupant load sensor, and FIG. 15B shows a cross section along a line B4—B4 in FIG. 15A. An occupant load sensor 110 is constituted by a main body portion 120 receiving a displacement sensor 112, an upper bolt portion 132 fixed, for example, to a seat rail side, and a lower bolt portion 134 fixed to a rail mount side. A strain surface 114 allowed to be deflected microscopically by the load is provided within the main body portion 120, and the displacement sensor 112 is arranged in the strain surface 114. In this structure, since it is not necessary to vertically reciprocate the seat, it is possible to obtain a necessary seat strength by manufacturing an entire occupant load sensor by a metal without using the displacement regulating mechanism as in the publication 1.
However, in the structure shown in FIG. 15, in the case that an accuracy of an attaching position of the seat rail with respect to the floor side rail mount is low, the occupant load sensor is attached in a state in which the occupant load sensor is inclined, and in a state in which a force in the other directions than a vertical direction is applied, so that there is a problem that a measuring accuracy is lowered.
The present invention is made for the purpose of solving the problem mentioned above, and an object of the present invention is to provide an occupant load sensor which can improve a detecting performance on the basis of a simple structure.